Solution Cloudy Skies Are Common

Whenever polls are taken of such things, Asimov's Nightfall is routinely voted as the greatest piece of SF below novel length. It tells the story of scientists on Lagash, a planet in a system of six stars. In reality, the chaotic orbit of Lagash would not allow the development of advanced life-forms. For the sake of the story, however, Asimov postulates that intelligent, technically advanced creatures have developed on the planet. Physicists there have recently discovered the law of universal gravitation, so they can predict the position of any of the six suns of Lagash. Their new knowledge also enables them to deduce the existence of a moon orbiting Lagash. The presence of the moon has to be deduced because it is not visible: having six suns means darkness never falls on Lagash. The planet never has night. Nightfall describes what happens on Lagash when a rare alignment of the moon and the six stars produces an eclipse, and the beings of Lagash for the first time see the night sky. It is a wonderful story.174

The astronomers on Lagash would find it difficult to develop what we call astronomy. Since light from their six suns drowns out light from any other astronomical body, they could not know of the existence of planets or stars. Historically, on Earth, the development of physical science depended critically upon having planets whose orbits scientists tried to explain. Without a clear view of the skies, how could Lagash astronomers possibly develop an understanding of the physical Universe or of their place in it? They could be our superiors in terms of intelligence, they might develop a technology beyond our own, but they would not attempt to contact us because they would not know of or even suspect our existence.

Although the situation in Nightfall is unlikely, one can think of many cases where the physical environment of an ETC would prevent them ever developing the notion that beings exist on other worlds. What if, as one philosopher asked, cloudy skies are common? No matter how intelligent the species, no matter how good its technology, those beings might never develop an understanding of the Universe beyond their planet. Interstellar communication would not take place. Perhaps there are thousands of ETCs out there — but they are behind cloud cover, or stuck near the Galactic center where the sky is eternally bright, or in any of a hundred environments that would render astronomy difficult. Does this explain the paradox?

This idea has made for some of the greatest SF stories, but it is difficult to accept it as an explanation of the Fermi paradox. As we shall see later, we do not know how many habitable planets exist — but we do know that the number is probably large. It is inconceivable that Earth is the only planetary environment with a clear view of the skies!